In endoscopic surgical procedures, relatively narrow surgical instruments are inserted into a patient's body so that the distal ends of the instruments are positioned at a remote interior site, while the proximal ends of the instruments remain outside the patient's body. The surgeon manipulates the proximal ends of the instruments as required to cause the distal ends of the instruments to carry out the desired surgical procedure at the remote interior site.
In order to visualize the remote interior site, the surgeon also inserts an endoscope into the body during the endoscopic surgery, together with, or including, an appropriate source of illumination.
The endoscope generally comprises an elongated shaft having a distal end and a proximal end, and an internal passageway extending between the distal and proximal ends. At the distal end is disposed a window and proximate thereto, within the shaft, is disposed an image capturing means, such as an objective lens and, proximally thereof, image conveying means, such as relay lenses. The latter extend through the internal passageway of the shaft. Accordingly, the image capturing means captures an image of a selected region located substantially adjacent the distal end of the shaft, and the image conveying means relays the image provided by the image capturing means to the proximal end of the shaft. Viewing means, such as one or more eye pieces, or electronic display apparatus, disposed adjacent the proximal end of the shaft, present the image obtained by the image capturing means and conveyed by the image conveying means, in such manner as to be viewed by the surgeon.
The image capturing means, conveying means, and viewing means commonly utilize one of several different arrangements to capture an image at the distal end of the shaft and to present it to the surgeon.
For example, in one arrangement, the image capturing means comprise a bundle of fiber optic filaments which extend through the internal passageway of the shaft. A front window and an objective lens are positioned at the distal end of the shaft to focus the desired image onto the distal end of the fiber optic bundle. The fiber optic bundle conveys the captured image to the proximal end of the shaft, where it is received by viewing means. In this arrangement, the viewing means may comprise a conventional optical viewer, or eyepiece, which is viewed directly by the surgeon. Alternatively, the viewing means may comprise an appropriate image sensor, e.g., a charge coupled device (CCD), or video tube, which can receive the captured image from the proximal end of the fiber optic bundle and generate corresponding video signals representative of the captured image. The video signals are then displayed on an appropriate display device (e.g., a monitor) which is viewed by the surgeon.
In a second arrangement, the image capturing means comprise a CCD which is disposed at the distal end of the shaft, and wires for conveying the image extend through the internal passageway of the shaft. An appropriate objective lens, behind a front window, focuses the desired image onto the CCD image-receiving surface, and the wires convey the CCD element video output signals to the proximal end of the shaft. The video signals are then displayed on an appropriate display device which is viewed by the surgeon.
In a third arrangement, the image capturing means comprise a front rod-lens system. In this embodiment, an objective lens, behind a front window, focuses the desired image onto the first of a series of rod-lens elements arranged within the internal passageway of the shaft so as to capture the desired image at the distal end of the shaft and convey that image to viewing means located at the proximal end of the shaft. With this arrangement, the viewing means can comprise a display device in the form of a conventional optical viewer, or eyepiece, which is viewed directly by the surgeon. Alternatively, the viewing means can comprise an appropriate image sensor, e.g., a CCD element or video tube, which can receive the captured image from the proximal end of the rod-lens system and generate corresponding video signals which are representative of the captured image. These video signals are then displayed on an appropriate display device viewed by the surgeon.
Some of the above and other combinations of image capturing, conveying and viewing means are disclosed in U.S. Pat. No. 4,491,865, issued Jan. 1, 1985 to D. Dana et al; U.S. Pat. No. 4,867,137, issued Sep. 19, 1985 to Y. Takahashi; U.S. Pat. No. 4,879,992, issued Nov. 14, 1989 to S. Nishigaki et al; and U.S. Pat. No. 4,364,629, issued Dec. 21, 1982 to W. H. Lang et al.
Regardless of the particular construction involved, all prior art endoscope viewing systems tend to suffer from a significant deficiency. When an endoscope at room temperature is inserted into a patient, the difference in temperature between the room and the patient's body usually is such as to cause fogging of the front window of the endoscope. Regardless of the type of image capturing, conveying and viewing means utilized, a window occluded by fog prevents the presentation of a clear view to the surgeon.
Under current practices, the fogging problem is addressed by pre-heating the window and/or pre-treating the window with an anti-fogging agent. In addition, the endoscope often is removed from the working environment and cleaned with a cloth, or the like. The pre-heating, pre-treating, and cleaning must be carried out with sterile materials, using sterile techniques. Such practices lead to increased costs and generate biohazardous wastes.
Thus, there is a need for an endoscope in which the front window is self-maintained fog-free in the presence of substantial differences between room temperature and patient body temperature.